Electroscopic printing powder

ABSTRACT

A developer mix for use in electrostatic printing to develop latent images, including charged and uncharged areas of an image bearing sheet said developer mix comprising separate granular carrier particles, and a developer powder comprising a coloring agent and a resin having a triboelectric relationship of opposite polarity with respect to said carrier granules, said resin comprising a blend of resins in which the physical properties of the blend are distinct with respect to the physical properties of the resin components which are heat blended together, the principal resin being a polyamide resin which represents the infrangible resin component, and the completed resin being reduced to a melt point within the range of 8*, whereby developed images of substantially improved black density may be formed over extended operating periods.

O United States Patent [191 1111 3,764,538

Shelffo Oct. 9, 1973 [54] ELECTROSCOPIC PRINTING POWDER 2,867,592 1/1959 Morris et al. 260/18 PN 1 new Loren Show Palatine, 533333 131322 22352335.: .113: 328112 1 2 [73] Assignee: Addressograph-Multigraph Corporation, Cleveland, Ohio Primary Examiner-Norman G. Torchin Assistant Examiner-J. P. Brammer [22] Filed 1971 Att0rneyS0l L. Goldstein [21] Appl. No.: 123,065

Related U.S. Application Data ABSTRACT [63] Continuation of Ser. No. 692,732, Dec. 22, 1967, A developer mix for use in electrostatic printing to den n h h is a n in i n-in-p r f Sen velop latent images, including charged and uncharged 357,743. P" 1 1964, abandoned areas of an image bearing sheet said developer mix comprising separate granular carrier particles, and a [52] U.S. Cl 252/62.1, 260/18, 260/19 developer der comprising a coloring agent and a [51] Int. Cl G03g 9/02 resin having a triboeieciric relationship f opposite [58] Field of Search 252/62.1; 260/18, polarity with respect to Said carrier granules, Said resin 260/18 19 comprising a blend of resins in which the physical properties of the blend are distinct with respect to the [56] References Cited physical properties of the resin components which are UNITED STATES PATENTS heat blended together, the principal resin being a 2,221,776 11 1940 Carlson 252/62.1 x Polyamide resin'whieh represents the infrangible resin 2,297,691 10/1942 Carlson 252/62.1 x mp n nt, an th mpleted resin being reduced to 2,899,335 8/1959 Straughan... 252/62.l X a melt point within the range of 8, whereby devel- 2,940,934 6/1960 Carlson 252/62 1 oped images of substantially improved black density 3,060,051 l0/l962 Johnson et al. 252/62.l X may b f d over d d operating i d 3,093,039 6/1963 Rheinfrank 252/62.l X 3,345,294 10/1967 Cooper 252/62.1 X 15 Claims, No Drawings ELECTROSCOPIC PRINTING POWDER CROSS-REFERENCE TO RELATED APPLICATIONS This application is a Continuation of my copending application Ser. No. 692,732, filed Dec. 22, 1967 now abandoned, which in turn is a Continuation-in-Part of the prior copending application Ser. No. 357,743, filed Apr. 6, 1964 now abandoned.

This invention relates to electroscopic powders of the type useful in rendering visible the latent electrostatic images produced by photoelectrostatic or electrostatic copying. More particularly it relates to improved electroscopic powders for use in automated type photoelectrostaticcopying apparatus.

In photoelectrostatic copying processes, an electrostatic charge pattern is created on a charged photoconductive layer, such as zinc oxide or selenium, by exposure to a light pattern. Various techniques and devices have been employed to expose the charged surface, such as projection or contact printing methods, fiber optic imaging devices, and various phosphor display devices. Upon exposure of the charged layer to light under darkroom conditions, a latent electrostatic charge image is formed.

Still other image generating devices are employed that directly deposit a charge pattern corresponding to the graphic subject matter by the use of single or multiple styli. The technique of direct imaging may be carried out in the presence of light.

Irrespective of the technique employed for creating a latent electrostatic charge image, it must be rendered visible by development with a suitable resinous, thermoplastic, electroscopic powder and rendered permanent by the application of heat, pressure, solvent vapor or other fixing technique. The developed image may be fixed in place on the surface upon which it is formed, or it may be transferred to a new surface and fixed thereon.

A number of techniques are available and in wide use for carrying out the developing step which brings the electroscopic powder, or toner powder as it is known in the art, into contact with said latent image. These include, for example, powder cascade, powder cloud, and dry magnetic brush development. The advancement represented by the improved electroscopic powders of this invention is applicable to all of the foregoing systems where a charge-sensing powder is brought into contact with an electrostatically charged surface for the purpose of producing a visible image.

Further discussion of the improvements represented by this invention will be explained in terms of the magnetic brush type of apparatus, but the novel electroscopic powders disclosed herein can also be used with equal advantage in other developing apparatus and their use is not limited to magnetic brush technique.

The magnetic brush method for developing an electrostatic image involves the use of a mixture of magnetically attractable particles and electroscopic powder. This mixture or developer mix is formed up into a brush-like mass on the surface of a cylindrical roll under the influence ofa magnetic field created by magnetic means disposed within said roll.

The electroscopic powder is held to the magnetically attractable carrier particles by a triboelectric effect which results from frictional contact between the particles. This effect is more fully described in U. S. Pat. No.

2.874,063 dated Feb. 17, 1959. The relative position in the triboelectric series of carrier and electroscopic powder materials will determine the polarity of the charge generated on the electroscopic powder. Hence, particular materials can be selected for either positive or reversal printing. In practice, the electroscopic powders are mixed with larger carrier particles, such as iron, ferrites, magnetites, cobalt, and nickel. The carrier particles align themselves along the lines of magnetic flux provided by the magnetic means so that they stand erect on the surface of the cylinder. In this manner the particles, carrying the electroscopic powder present a uniform and continuous array of developer mix along that portion of the roll which contacts the electrostatic recording member bearing the latent electrostatic image thereon.

U. S. Pat. No. 3,003,462 discloses a typical magnetic brush development apparatus wherein the developer mix is deposited in a trough, thereafter is picked up on the periphery of an applicating cylinder having the magnetic means therein, and is formed into a brush in the environment of said magnetic field. As the rotating applicator cylinder carries the developer mix outside the magnetic field, the magnetic brush collapses and developer mix falls back into the reservoir. This cycle of brush formation and collapse is repeated as long as the developer roll rotates.

Electroscopic powders available heretofore have left much to be desired when used in automated electrostatic copying machines, particularly where the magnetic brush-type apparatus is employed. One of the major problems is that of deterioration of the electroscopic powder components of the developer mix. One evidence of such deterioration appears in the photoelectrostatic copies which begin to show adherence of the electroscopic powder indiscriminately in both image and non-image areas.

Another evidence of mix deterioration is a fall-off or loss in copy density, that is, the developed image appears gray rather than having an intense black color.

Also, carrier particles may begin to deposit on the copy sheet as a result of mix deterioration giving the photoelectrostatic copy of a gritty feel.

Still further problems caused by mix deterioration relate to improper mixing and impairment of the mechanical mixing means of the developer apparatus.

The automated photoelectrostatic office copying equipment under discussion is designed especially for high production, high quality copying. Equipment of this type is required to produce up to 6000 copies in a typical work day. The deteriorated condition referred to above can take place rapidly. Deterioration of known developer mixes has heretofore necessitated complete and frequent replacement with fresh material.

Deterioration is caused by physical changes in the electroscopic powder. These physical changes primarily concern the particle size of the powder. The first such change relates to particle size fracture or comminution, and the second relates to agglomeration or clumping of small particles into larger ones.

The forces which operate in the magnetic brush developer exert a grinding or milling action on the developer mix. Electroscopic powder particles may be split or fractured so that the new fragments do not have the same electroscopic properties as the particles from which they were formed. Each of these fragments is present as a spurious particle which serves only to impair the performance of the developer system.

Further attrition of the particulate matter generates excessively small particles referred to as dust or fines that are incapable of discriminating between the charged and uncharged areas. These fines tend to become airborne and create an undesirable condition from a housekeeping standpoint.

Agglomeration or clumping is caused by an increase in mix temperature. This temperature rise may be due to the absorption by the powder of frictional energy developed through impact between the particles as they are mixed and churned within the developer unit. Another source of heat is the high temperature fusing unit within the apparatus. The thermoplastic toner particles begin to clump or agglomerate as they reach their softening or tackifying temperature. In a severe condition the agglomerates may occlude some of the iron carrier particles. These clumps, containing both iron and softened electroscopic powder, completely disrupt the developing step.

These clumps often become deposited in clearances between moving and stationary mechanical parts thereby increasing the powder required to drive the magnetic brush roller. The additional power is dissipated as heat so that the process of agglomeration becomes progressively worse.

Generation of the triboelectric charge on the electroscopic powder depends upon proper contact between toner and carrier particles. Clumping and agglomeration prevent the proper circulation and blending of toner with the carrier in the developer apparatus. A free-flowing condition is particularly necessary during replenishment when fresh toner is added to a depleted mix. Poor circulation gives rise to a non-uniform powder mixture which produces copies that are unevenly developed. Poor blending of electroscopic powder and iron particles reduces the level of triboelectric charge generated on the powder.

The demands placed on electroscopic powders suitable for high speed, continuous automatic electrostatic copying, are exacting and have heretofore not been met. From the foregoing discussion, it is seen that the thermosplastic, resinous toner particles must have certain distinct properties if it is to achieve a practical mix life in a magnetic brush developing apparatus.

The resin blend should be sharp-melting so that it is converted from discrete, solid pieces to a flowable material over a temperature range not greater than about 50 to 8F. Such a resin blend will flow smoothly onto the paper to form a permanent image and solidify rapidly when removed from the fuser, thus producing an image which will not smear. The thermosplasticresin should remain in a solid state at temperatures substantially higher than room temperature so that it does not soften, become tacky, and form cakes, clumps, or agglomerates. Such a divergence of requirements demands that the thermosplastic resin be at once tough and resilient enough to withstand the grinding action in the developer apparatus, yet sufficiently brittle and frangible to permit its reduction to powder on conventional grinding equipment.

Some thermoplastic compositions, which are tough and infrangible, have excellent electroscopic properties, but cannot be manufactured on conventional milling equipment. Other resins which may have excellent electroscopic properties and which may be readily ground to a desired particle size in conventional milling equipment are too brittle or frangible for the magnetic brush apparatus. These are reduced to an inordinate amount of dust and fines by the mixing action of the developer unit.

It is a primary object of this invention to provide an electroscopic powder particularly suitable for use in automated and continuous photoelectrostatic copying machines.

It is an object of this invention to provide an electroscopic developing powder having greatly improved resistance to deterioration in magnetic brush developer apparatus.

It is a further object of this invention to provide an electroscopic developing powder that will fuse in a narrow temperature range below the char point of paper and will resist clumping or agglomeration.

It is a further object of this invention to provide electroscopic developing powder which is resistant to attrition or grinding when used in a magnetic brush developer apparatus.

It is a still further object of this invention to provide an electroscopic developing powder comprised of a blend of thermoplastic resins having suitable frangibility properties and temperature response characteristics that will produce consistently high quality electrostatic copies having a high contrast between image and nonimage areas.

These and other objects are apparent from and are achieved in accordance with the following disclosure.

The electroscopic powders which constitute this invention comprise a blend of a tough, infrangible synthetic resin with a highly frangible thermosplastic synthetic resin which melts between about C. (158F.) and 165C. (329F.), preferably in the range of 2l3235F., said blend having the critical property of going from discrete particles to flowable material in a range from 5-8F. The blend of synthetic thermoplastic resin materials preferably should have a correspondingly high softening point, that is, the thermoplastic particles should remain discrete at temperatures up to F. and not adhere to one another or form agglomerates. The preferred average particle size of the electroscopic powder ranges from 4 to 10 microns with the over-all range of particle sizes ranging from 1 micron to 74 microns.

The invention is directed to a novel thermosplastic resinous electroscopic powder comprising a tough, infrangible resin component, such as a thermoplastic polyamide resin, which is chemically blended with a highly frangible, brittle substance such as a rosinmodified maleic anhydride-polyhydric alcohol resin, an unsaturated co-ester resin such as a diphenol resin esterified with a fatty acid, or a pure non-heat reactive phenolic resin.

The powder blends may optionally include additives such as polyol resins, toluenesulfonamides, or butylated-hydroxy-toluene which enter into the blends as fluxing agents, tending to decrease the melt viscosity of the thermoplastic blend. I

The preferred polyamide resins are produced by the reaction of high molecular weight polyene fatty acids and their esters with an amine. By reacting ammonia, a primary or secondary amine, a hydroxyamine or an alkanolamine, with a high molecular weight carboxylic acid or an ester thereof, either saturated or unsaturated, said acid or ester being obtainable by polymerizing at elevated temperature said polyene fatty acid or esters thereof, and in the case of the esters, converting the polymers to the corresponding acid if desired, there are produced the preferred polyamides. Examples of polyene fatty acids in esterified form are 9,1land/or 9,12-octadecadienoic acid (obtainable from soybean oil and dehydrated castor oil), linoleic acid, alpha and beta-eleostearic acid (obtainable from tung oil). The preferred esters are those derived from methanol, ethanol, and propanol. Primary or secondary amines may be used such as, for example, methylamine, ethylamine, propylamine, ethylenediamine, tetraamethylenediamine, pentamethylenediamine, piperazine, and diethylenetriamine. The class of thermoplastic, polyamide resins is disclosed in U. S. Pat. No. 2,379,413 and sold by the General Mills Company under the trademarks Versamide and Omamid. Other suitable polyamide resins are also available from the Krumbhaar Resin Division of Lawter Chemicals, Inc., under the trademark Polymid.

The second thermoplastic constituent in the electroscopic powder is extremely frangible but it is sharp melting. A suitable frangible constituent may be a rosin-modified phenolic resin, such as those prepared by modifying a phenol formaldehyde resin with the reaction product of maleic anhydride and rosin or a polyhydric alcohol such as glycerol or pentaerythrytol. Such rosin-modified phenolic resins are sold under the trademark Amberol" by Rohm & Hass Company. Diphenolic resin materials esterified with a soya fatty acid and certain thermoplastic phenolformaldehyde resins exhibit satisfactory frangible properties. The esterified diphenolics are available from the Johnson Wax Company Chemical Division of Racine, Wisconsin, and the thermoplastic phenol-formaldehyde resins are available from the Krumbhaar Resin Division of Lawter Chemicals, Inc., and from Nelio Chemicals, Inc., Jacksonville, Florida, as their VBR-800 series resins.

The blend of infrangible and frangible resins with coloring materials forming the electroscopic powder should be highly infrangible and should have a fracturing value of at least 400 grams-centimeters when measured on a wafer of resin 3.75 cm. in diameter and 0.5 cm. in thickness at 100F. by the falling ball method. In this method, as adapted from American Institute of Mining and Metallurgical Engineers, Vol. 87, p. 35, 1930, the resin wafer is subjected to impact by a falling ball and the energy (measured in gram-centimeters) required to just fracture the wafer is measured. The infrangible resin component of the resin blend should preferably have a fracturing value of at least 1000 gram-centimeters in the foregoing test while the frangible resin component may have low fracturing values in the range of 100-200 gram-centimeters.

The resin blend forming the electroscopic powder should not soften or become tacky at temperatures below 130F. The softening properties of resins can be measured with a penetrometer by the procedure of A.S.T.M. Standard No. D5-61. By this procedure, it has been found that resin blends which permit a maximum penetration not greater than 1.0 millimeter at 130F. with a standard needle (No. 4103) in a standard Lab- Line" penetrometer (No. 4100) at a force of 100 grams for 5 seconds resist softening and do not clump or agglomerate during use as electroscopic powder.

The action of the fluxing agent, as an optional component, is believed to lower the melting point of the blend without broadening the melting point range. Successful fluxing agents are provided by the group of polyhydric alcohols sold by the Shell Chemical Company under the trademark "Polyol X-450 of the general formula i al-I5 n FORMULATION NO. 1

(Major percentage of tough, infrangible resin) Polyamide Resin 5090% Frangible resin component (phenollic maleic anhydridepolyhydric alcohol resin) 5-40% Polyols OI0% Nubian resin black l-5% Carbon black pigment (Neo-spectra, Mark III) l-5% FORMULATION NO. 2

(Minor percentage of tough, infrangible resin) Polyamide Resin 9-50% Frangible resin component (Pure phenolics Krumbhaar K-254) 50-90% Polyols O-10% Nubian resin black l-6% Carbon black pigment (Neo-spectra, Mark III) l-2% The following examples are given to illustrate preferred embodiments and process for producing electroscopic powders embodying this invention. It will be understood that this invention is not limited to these examples.

In these examples, all percentages are given on a weight basis.

EXAMPLE 1 Electroscopic powder formulation is:

Synthetic, polyamide, thermoplastic resin (Versamide 930) 33% Polyol (Shell X-450) 9.9% Maleic anhydride-polyhydric alcohol rosin-modified resin (Amberol 800, Rohm & Haas Company) 49.5% Nubian resin black dye 6.6% Carbon black pigment (Neo-spectra, Mark II) l.0%

The quantity of polyamide resin called for is heated in a suitable vessel equipped with a conventional impeller type mixer until the resin is just molten so that it can be stirred. To the molten polyamide resin is added the Polyol while the mass is being agitated. Agitation continues during the addition of the maleic anhydridepolyhydric alcohol rosin-modified resin. After the maleic anhydride-polyhydric alochol resin is completely melted, the quantityof black dye is added to the batch followed by the addition of the carbon black.

After the batch has been thoroughly mixed, it is removed from the mixing vessel, cooled, crushed and pulverized to an average particle size ranging from 4 to 10 microns. Understandably there will be particle sizes ranging from under one micron to 50 microns and larger. As a final step, the electroscopic powder is passed through a 200 mesh screen so that the largest particle size possible in such an electroscopic powder would be under 75 microns.

The softening point of the electroscopic powder was measured by placing a quantity of the electroscopic powders in a constant temperature oven for 12 hours. A series of oven tests, at different temperature levels, revealed that powder produced in Example I remained in particulate form, and did not clump or agglomerate until tested at a 155F. level. The melt point of the electroscopic powder was in the range of 2l5-220F. measured in accordance with A.S.T.M. Method No. E28- 5ST.

The electroscopic powder was combined with iron particles in a ratio of one part powder to 15 parts iron, making a developer mix suitable for developing electrostatic images. The developer mix was charged into the developer unit of a photoelectrostatic copier. More than 50,000 copies were developed with this developer mix requiring the periodic addition of fresh electroscopic powder to replace the amount taken out by the making of copies. Otherwise the developer unit did not require servicing such as complete replacement of the charge, or cleaning of the unit to remove clumps or agglomerates.

The image copies were of uniform density indicating complete and thorough mixing between the carrier and powder. A high image density was maintained throughout the run while non-image areas maintained clean and free of spurious toner deposition. A copy is considered to have proper image density if reflectance density measurements, taken by a standard Photovoltmeter, are above 1.0 units.

Similarly, reflectance readings can give a measure of the contrast between the image and non-image areas. The non-image area on a processed copy should not measure more than 0.05 Photovolt units. The copies were clean in the non-image areas giving Photovolt reading less than 0.05 units.

The copies were not gritty indicating that the carrier particles were being retained in the system and not occluding on the powder.

EXAMPLE 2 Ingredients:

Polyamide resin (Versamide 930) 74% Maleic anhydride-polyhydric alcohol rosin-modified resin (Amberol 800) l9% Nubian resin black dye 5.6% Carbon black pigment (Neo-spectru, Mark ll) l.4%

The ingredients were processed in accordance with the steps set forth for Example 1 above. The melting point range and softening point of the above electroscopic powder were 2l3220F. and greater than 140F., respectively. It will be noted that this example incorporates a major percentage of the tough, infrangible polyamide material. Photovolt readings were all above 1.0 units. Such an electroscopic formulation finds particular utility in environments where the copying equipment is used for extended periods of time and where there is a high ambient temperature.

EXAMPLE 3 An electroscopic powder was prepared in accordance with the procedure of Example 1 wherein the electroscopic powder was comprised largely of polyamide material.

Ingredients:

Polyamide resin (Versamide 930) Maleic anhydride-polyhydric alcohol rosin-modified resin (Amberol 800) 7% Nigrosine dye 6% Polyols 8% Carbon black pigment (Nee-spectra, Mark II) 1% The melting point range and the softening point of the granular mass were 217-222F. and greater than F., respectively. The formulation of Example 3 is suitable for use under high temperature conditions. The inclusion of a fluxing agent tends to lower the melt point slightly and give a more uniform image.

EXAMPLE 4 Ingredients:

Polyamide resin (Versamide 930) 33% Polyol (Shell X-450) fluxing agent 9.9% Phenolic Resin (No. K-254 Krumbhaar Chem. Div. of Lawter Chemicals, Inc.) 49.5% Nubian resin black (National Aniline) 6.6% Carbon black pigment (Nee-spectra, Mark II) The above formula has substituted for the maleic anhydride rosin-modified resin a phenol-formaldehyde resin which is a highly frangible, sharp melting thermoplastic material. The performance of this formulation in respect of print quality and resistance to developer mix deterioration was fully equivalent to that observed in Example 1. The melting point range and softening point of the above example were 21 5-220F. and greater than l40F., respectively.

EXAMPLE 5 EXAMPLE 6 The electroscopic powder prepared in this example conformed to the formula set forth in Example 1 above with the exception that a mixture of orthoand para-N- ethyl-toluene-sulfonamides (Santicizer 8, Monsanto Chemical Company) was substituted as a fluxing agent for the polyol (Shell X450). The copy quality obtained was fully equivalent to the copy quality obtained from the formulation of Example 1.

EXAMPLE 7 This example differs from Example 1 chiefly in the use of lesser percentages of polyamide resin blended with the highly frangible thermoplastic material. It has been found that the addition of polyamide in amounts less than 9 percent by weight in the electrostatic powder formula has little or no effect on improving its resistance to the grinding and milling action present in the developer apparatus.

Polyamide resin (Versamide 930) 9% Maleic anhydride-polyhydric alcohol rosin-modified resin (Amberol 800) 83.2% Nubian resin black 6% Carbon black (Nee-spectra, Mark II) 1% The above composition had a melting point range and softening point of 220-228F. and above 155F., respectively. Electroscopic powders formulated with -6 percent polyamide deteriorated after 3,000-5,000 electrostatic prints. Improvements begin to show when the level of 9 percent, and above, of the polyamide thermoplastic synthetic resin is included in the formula.

All of the foregoing examples when used in the magnetic brush developer of the type described in U. S. Pat. No. 3,003,462 gave consistently dense uniform images. The first copy from a batch of developer mix, and the later copies made after 100 hours of continual use, produced prints having a print density greater than 1.0 Photovolt readings. Reflectance in the non-image area on the developed copy of photoelectrostatic paper was less than 0.05 Photovolt units.

With the developer mix of this invention, the formation of clouds of developer powder or throwout, in the vicinity of the developer mix, is greatly minimized, if not completely prevented. Hence, the areas where such machines are located are kept substantially clean.

A further advantage of the electroscopic powder of this invention is that it does not agglomerate or cake during storage, and therefore remains uniform, ready for use. It is not uncommon for materials in shipment to be exposed to a wide variety of climatic conditions, including extremely high temperatures, which often cause the powder to actually cake into a solid mass in the shipping container. The material of this invention has been found to retain its free-flowing granular consistency, making it ready for use immediately by the operator.

The discussion'of the electroscopic powder has been limited to the technique of positive printing wherein the triboelectric relationship of the electroscopic powder to the iron carrier particles is such that the particles acquire the necessary positive charge so that they will adhere to the negatively charged electrostatic image on the photoconductive member. The advantages provided by the electroscopic powders of this invention may be applied with equal success to the technique of reversal printing as described in co-pendingapplication Ser. No. 221,888 and assigned to the same assignee.

The present invention has been described in great detail, having presented the best mode of formulating the electroscopic powders. Other useful materials and formulations will occur to one skilled in the art over the particular embodiments described herein which are exemplary and not intended to limit the invention, but are intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. A developer mix for use in electrostatic printing to develop latent images including charged and uncharged areas of an image-bearing sheet, said developer mix comprising the combination of a. separate granular triboelectrically chargeable carrier particles, and

b. a developer powder comprising 1. a coloring agent selected from the group consisting of dyes and pigments, and

2. a resin blend having a triboelectric relationship of opposite polarity with respect to said carrier granules and having a sharp melting point within the range of about C. to about 165 C., said resin blend being formed by mixing the resin components in their molten state and being composed of i. an infrangible thermoplastic polyamide resin formed by reacting a high molecular weight polyene fatty acid or ester thereof with an amine said polyamide resin having a fracturing value of at least 1000 gram centimeters, and

ii. a highly frangible thermoplastic resin having a fracturing value not greater than 200 gram centimeters, said fracturing values being measured by the falling ball method on a wafer of resin maintained at F. and 3.75 centimeters in diameter and 0.5 centimeters in thickness, whereby developed images of substantially improved density can be formed over extended operating periods.

2. A developer mix for use in electrostatic printing to develop latent images including charged and uncharged areas of an image-bearing sheet, said developer mix comprising the combination of a. separate granular magnetically attractable carrier particles, and

b. a developer powder comprising 1. a coloring agent selected from the group consisting of dyes and pigments, and

2. a resin blend having a triboelectric relationship of opposite polarity with respect to said magnetically attractable granules and having a sharp melting point within the range of about 70C. to about C., said resin blend being formed by mixing the resin components in their molten state and being composed of I i. a major portion of an infrangible thermoplastic polyamide resin formed by reacting a high molecular weight polyene fatty acid or esters thereof with an amine, and

ii. a minor portion of a highly frangible thermoplastic resin having a fracturing value not greater than 200 gram centimeters, the frangibility of the resins being measured by the falling ball method on a wafer of resin maintained at 100 F. and 3.75 centimeters in diameter and 0.5 centimeters in thickness, whereby developed images of substantially improved density can be formed over extended operating periods.

3. A developer mix as defined by claim 2 wherein the frangible resin is a maleic anhydride rosin-modified resin.

4. An electroscopic powder suitable for developing electrostatic charge images, said powder consisting essentially of frangible and infrangible thermoplastic resins combined when in their molten state to form a miscible mixture, said mixture having physical properties which are distinct from either'of the components comprising said mixture, and having a melting range not greater than 8 F., a softening point not less than 130 F. and a melting point below the char point of paper to which it is applied, said frangible resin constituting 10 to 91 percent by weight of the electroscopic powder and having a fracturing value not greater than 200 grams centimeters, and said infrangible resin being a polyamide resin formed by reacting a high molecular weight polyene fatty acid or esters thereof with an amine and constituting to 90 percent by weight of the electroscopic powder and having a fracturing value of at least 1000 gram centimeters, the fracturing value of the resins being measured at 100 F. by the falling ball method on a wafer of resin 3.75 centimeters in diameter and 0.5 centimeters in thickness.

5. The electroscopic powder of claim 4 wherein said powder has a melting point in the range of from 215 to 235 F.

6. The electroscopic powder of claim 4 wherein said powder is comprised of from to 50 percent by weight of said polyamide resin and 50 to 90 percent of a maleicanhydride rosin-modified resin.

7. The electroscopic powder of claim 4 wherein said powder is comprised of from 30 to 40 percent polyamide and 40 to 50 percent maleic anhydride rosinmodified resin and from 1 to 10 percent polyhydric alcohol fluxing agents.

8. The electroscopic powder of claim 4 wherein said powder is comprised of from 50 to 90 percent of said thermoplastic infrangible polyamide resin and from 5 to 40 percent of a frangible thermoplastic resin component selected from the group consisting of maleic anhydride rosin-modified resin, esterified diphenolic resin, and phenol-formaldehyde resins.

9. The electroscopic powder of claim 4 wherein said powder has a particle size range of from 1 micron to 74 microns with an average particle size of from 4 microns to 10 microns.

10. A developer mix for use with magnetic brushtype developing apparatus for rendering latent electrostatic charge images visible on electrostatic recording members by applying thereto an electroscopic powder, and subsequently fixing the adhered powder thereto, said developer mix comprising a granular electroscopic powder of colored thermoplastic particles mixed with larger magnetically attractable carrier particles each having a charge of opposite polarity, said thermoplastic powder having as one component a polyamide resin formed by reacting a high molecular weight polyene fatty acid or esters thereof with an amine heat blended with a second frangible resin component to form a composite electroscopic powder having a fracturing value of at least 400 gram centimeters and said polyamide resin having a fracturing value of at least 1000 gram centimeters.

11. The developer mix as claimed in claim 10 wherein said polyamide resin is present in an amount of from 50 to percent by weight of said powder. 12. A developer mix as cliamed in claim 10 wherein the second component is maleic-anhydridepolyhydricalcohol rosin-modified resin in an amount of from 9 to 50 percent by weight of the electroscopic powder.

13. The developer mix as claimed in claim 11 wherein the polyamide resin is a reaction product of polymerized linoleic acid and ethylenediamine.

14. The developer mix as claimed in claim 10 wherein the electroscopic powder has an average particle size in the range of from 4 microns to 10 microns.

15. An improved electrostatic developer mix including carrier particles and colored toner particles, wherein the improvement comprises said toner particles being a hot melt blend of an infrangible thermoplastic resin and a frangible thermoplastic resin wherein physical properties of the resulting blend are distinct from the properties of either of the separate components, said infrangible resin material being a polyamide resin formed by reacting a high molecular weight polyene fatty acid or esters thereof with an amine said polyamide resin having a fracturing value of at least 1000 gram centimeters and said frangible material having a fracturing value less than 200 gram centimeters and the fracturing of the blend being at least 400 gram centimeters.

v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,754,538 Dated October 9 1973 Inventoflxi Loren E. Shelffo It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, Line 50, "50 should read "5 Column 7, Line 39, "maintained" should read "remained".

Column 8, Line 61, the numeral "19" after the period is not required.

Column 11, Line 30, after the word "percent" the words "by weight" should be inserted.

Signed and sealed this 2nd day of July 19%.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. Attesting Officer 0. MARSHALL DANN, Commissioner of Patents FORM PC4050 (10-69) uscoMM-Dc 60376P69 UTS. GOVERNMENT PRINTING OFFICE: 1989 O366'335 

2. a resin blend having a triboelectric relationship of opposite polarity with respect to said carrier granules and having a sharp melting point within the range of about 70* C. to about 165* C., said resin blend being formed by mixing the resin components in their molten state and being composed of i. an infrangible thermoplastic polyamide resin formed by reacting a high molecular weight polyene fatty acid or ester thereof with an amine said polyamide resin having a fracturing value of at least 1000 gram centimeters, and ii. a highly frangible thermoplastic resin having a fracturing value not greater than 200 gram centimeters, said fracturing values being measured by the falling ball method on a wafer of resin maintained at 100* F. and 3.75 centimeters in diameter and 0.5 centimeters in thickness, whereby developed images of substantially improved density can be formed over extended operating periods.
 2. A developer mix for use in electrostatic printing to develop latent images including charged and uncharged areas of an image-bearing sheet, said developer mix comprising the combination of a. separate granular magnetically attractable carrier particles, and b. a developer powder comprising
 2. a resin blend having a triboelectric relationship of opposite polarity with respect to said magnetically attractable granules and having a sharp melting point within the range of about 70*C. to about 165*C., said resin blend being formed by mixing the resin components in their molten state and being composed of i. a major portion of an infrangible thermoplastic polyamide resin formed by reacting a high molecular weight polyene fatty acid or esters thereof with an amine, and ii. a minor portion of a highly frangible thermo-plastic resin having a fracturing value not greater than 200 gram centimeters, the frangibility of the resins being measured by the falling ball method on a wafer of resin maintained at 100* F. and 3.75 centimeters in diameter and 0.5 centimeters in thickness, whereby developed images of substantially improved density can be formed over extended operating periods.
 3. A developer mix as defined by claim 2 wherein the frangible resin is a maleic anhydride rosin-modified resin.
 4. An electroscopic powder suitable for developing electrostatic charge images, said powder consisting essentially of frangible and infrangible thermoplastic resins combined when in their molten state to form a miscible mixture, said mixture having physical properties which are distinct from either of the components comprising said mixture, and having a melting range not greater than 8* F., a softening point not less than 130* F. and a melting point below the char point of paper to which it is applied, said frangible resin constituting 10 to 91 percent by weight of the electroscopic powder and having a fracturing value not greater than 200 grams centimeters, and said infrangible resin being a polyamide resin formed by reacting a high molecular weight polyene fatty acid or esters thereof with an amine and constituting 5 to 90 percent by weight of the electroscopic powder and having a fracturing value of at least 1000 gram centimeters, the fracturing value of the resins being measured at 100* F. by the falling ball method on a wafer of resin 3.75 centimeters in diameter and 0.5 centimeters in thickness.
 5. The electroscopic powder of claim 4 wherein said powder has a melting point in the range of from 215* to 235* F.
 6. The electroscopic powder of claim 4 wherein said powder is comprised of from 10 to 50 percent by weight of said polyamide resin and 50 to 90 percent by weight of a maleic anhydride rosin-modified resin.
 7. The electroscopic powder of claim 4 wherein said powder is comprised of from 30 to 40 percent polyamide and 40 to 50 percent maleic anhydride rosin-modified resin and from 1 to 10 percent polyhydric alcohol fluxing agents.
 8. The electroscopic powder of claim 4 wherein said powder is comprised of from 50 to 90 percent of said thermoplastic infrangible polyamide resin and from 5 to 40 percent of a frangible thermoplastic resin component selected from the group consisting of maleic anhydride rosin-modified resin, esterified diphenolic resin, and phenol-formaldehyde resins.
 9. The electroscopic powder of claim 4 wherein said powder has a particle size range of from 1 micron to 74 microns with an average particle size of from 4 microns to 10 microns.
 10. A developer mix for use with magnetic brush-type developing apparatus for rendering latent electrostatic charge images visible on electrostatic recording members by applying thereto an electroscopic powder, and subsequently fixing the adhered powder thereto, said developer mix comprising a granular electroscopic powder of colored thermoplastic particles mixed with larger magnetically attractable carrier particles each having a charge of opposite polarity, said thermoplastic powder having as one component a polyamide resin formed by reacting a high molecular weight polyene fatty acid or esters thereof with an amine heat blended with a second frangible resin component to form a composite electroscopic powder having a fracturing value of at least 400 gram centimeters and said polyamide resin having a fracturing value of at least 1000 gram centimeters.
 11. The developer mix as claimed in claim 10 wherein said polyamide resin is present in an amount of from 50 to 90 percent by weight of said powder.
 12. A developer mix as claimed in claim 10 wherein the second component is maleic-anhydride-polyhydricalcohol rosin-modified resin in an amount of from 9 to 50 percent by weight of the electroscopic powder.
 13. The developer mix as claimed in claim 11 wherein the polyamide resin is a reaction product of polymerized linoleic acid and ethylenediamine.
 14. The developer mix as claimed in claim 10 wherein the electroscopic powder has an average particle size in the range of from 4 microns to 10 microns.
 15. An improved electrostatic developer mix including carrier particles and colored toner particles, wherein the improvement comprises said toner particles being a hot melt blend of an infrangible thermoplastic resin and a frangible thermoplastic resin wherein physical properties of the resulting blend are distinct from the properties of either of the separate components, said infrangible resin material being a polyamide resin formed by reacting a high molecular weight polyene fatty acid or esters thereof with an amine said polyamide resin having a fracturing value of at least 1000 gram centimeters and said frangible material having a fracturing value less than 200 gram centimeters and the fracturing of the blend being at least 400 gram centimeters. 